(1) Field of the Invention
The present invention relates to fabrication processes used to create a dynamic random access memory, (DRAM), device, on a semiconductor substrate, and more specifically, relates to a process used to create a crown shaped storage node structure, for the DRAM device.
(2) Description of Prior Art
Cylindrical shaped, or crown shaped, capacitor structures, have been used to increase the surface area of DRAM capacitors, and thus increase the signal or performance of DRAM devices. Stacked capacitor structures, (STC), located overlying the transfer gate transistor, of the DRAM device, are limited by the dimensions of the underlying transfer gate transistor. Therefore to increase the surface area of the STC structure, without infringing on neighboring, underlying transfer gate transistors, specific STC shapes are employed. For example, a crown shaped storage node structure, comprised of vertical polysilicon features, connected to an underlying horizontal polysilicon feature, offers increased storage node surface area, when compared to counterparts, fabricated without vertical polysilicon features, or without the use of the crown shape. The use of sub-micron features, for high density DRAM cells, however can create concerns in terms of photolithographic alignments. For example if the crown shaped storage node structure is mis-aligned to an underlying conductive plug structure, where the conductive plug is used to allow communication between an overlying STC structure and an underlying conductive region in the semiconductor substrate, unwanted undercutting of passivating dielectric layers can result during the procedures used to fabricate the crown shaped storage node structure. These undercut regions of dielectric layer can result in yield and reliability difficulties, when completing the capacitor structure.
This invention will offer a process in which mis-alignment of a crown shaped storage node structure, to a storage node contact hole, can be tolerated without yield or reliability concerns. This invention features the final definition of a storage node contact plug structure, after definition of the crown shaped storage node structure, and after removal of an insulator shape, used for definition of the crown shaped storage node structure. Therefore unpatterned polysilicon, used for a top portion of a storage node contact plug structure, remains to protect underlying dielectric layers, during the removal of the insulator shape used for definition of the crown shaped storage node structure. Prior art, such as Wang et al, in U.S. Pat. No. 5,759,892, describe the use of spacers to allow for mis-alignments, however that prior art, when compared to the simpler, and different process, offered in this invention, adds complexity and cost.